An installation cost, an installation space and an operation cost for a horizontal continuous casting apparatus are less than those for a vertical continuous casting apparatus. In addition, no stresses occur due to a bending of a cast piece, and a bulging is less liable to occur because of a small internal pressure of the cast piece. An economic efficiency is good particularly for a casting equipment of a small capacity. Therefore, recently, the horizontal continuous casting apparatuses have been put into practical use for casting billets and the like.
FIG. 1 is a vertical cross-sectional view of a main portion of a horizontal continuous casting apparatus of a general type. As shown in the drawing, in the horizontal continuous casting apparatus, a tundish 21 is connected to a mold 1 via a tundish nozzle 10, a sliding nozzle 12 and a feed nozzle 3. Each of the tundish 21, the tundish nozzle 10, the sliding nozzle 12 and the feed nozzle 3 is made of an ordinary refractory of a zircon type or an alumina type. The mold 1 is composed of a front-stage mold 23 and a rear-stage mold 24, and is cooled by cooling water W. The front-stage mold 23 is made of copper, and a break ring 2 is mounted on the inlet side thereof. The break ring 2 is made of heat-resistant ceramics such as boron nitride and silicon nitride. The rear-stage mold 24 is made of graphite. Depending on the type of apparatus, the sliding nozzle 12 may not be provided.
A molten material M supplied into the mold 1 is cooled by the inner peripheral surface of the mold to form a solidification shell S. The formation of the solidification shell S begins uniformly in its cross-section due to the break ring 2. The break ring 2 prevents the solidification shell S from growing in a reverse direction, that is, toward the feed nozzle 3. A cast piece C, formed as a result of solidification of the molten material M, is intermittently withdrawn from the outlet side of the mold 1 by a withdrawing device (not shown) such as pinch rolls. When the cast piece is intermittently withdrawn, a space is formed between the break ring 2 and the end of the solidification shell S, and a fresh supply of the molten material M flows into this space to form a fresh solidification shell S.
The above space is under a negative pressure, and the sliding nozzle 12 and the feed nozzle 3, as well as the feed nozzle 3 and the break ring 2, are merely joined together at their end surfaces, and the front-stage mold 23 and the break ring 2 are merely fitted together. Therefore, the air intrudes into the space through these joint surfaces. The intruding air is included in the molten material M, and remains in the surface or the interior of the cast piece to be a cause for a casting defect such as a blow hole.
In order to solve this problem, there is provided a horizontal continuous casting apparatus as disclosed in Japanese Patent Unexamined Publication No. 58-74256 and Japanese Patent Unexamined Publication No. 59-66959.
The horizontal continuous casting apparatus of Japanese Patent Unexamined Publication No. 58-74256 comprises a ladle and a tundish disposed beneath it, and a sealed chamber surrounded by a seal member is provided between the bottom surface of the ladle and the upper surface of the tundish. A mold is, together with a nozzle, integral with the tundish and inert gas is supplied into the above sealed chamber. In this apparatus, the inert gas prevents the air from intruding into the tundish, the nozzle, the mold and the like.
The horizontal continuous casting apparatus of Japanese Patent Unexamined Publication No. 59-66959 comprises a device including a seal cover portion covering a nozzle and at least part of the boundary surface between the nozzle and a mold, and an inert gas injection device covering the nozzle and the boundary surface to provide a gas seal. In this apparatus, in the vicinity of the inlets of the nozzle and the mold, the molten metal of elevated temperatures is prevented by the inert gas from coming into contact with the atmosphere.
There exists a horizontal continuous casting apparatus in which in order to facilitate the exchange and maintenance of a nozzle, a break ring or a mold, one of a tundish and the mold is movable whereas the other is fixed. In such an apparatus, the movable side is driven by a hydraulic cylinder or the like to advance to be connected to the fixed side. For example, in a horizontal continuous casting apparatus disclosed in Japanese Patent Unexamined Publication No. 53-88630, a carriage carrying a tundish is driven by a hydraulic cylinder to advance, so that a tundish nozzle is connected to a mold via a nozzle. In contrast, in a horizontal continuous casting apparatus disclosed in Japanese Patent Unexamined Publication No. 58-168457, a carriage carrying a mold is driven by a hydraulic cylinder to advance to be connected to a tundish via a nozzle.
In any of the above conventional horizontal continuous casting apparatuses, a seal is not provided near the mold inlet, and therefore there is encountered a problem that the air intrudes into the mold as described above, so that a casting defect develops.
Further, in the above conventional horizontal continuous casting apparatus provided with the seal device near the mold inlet, the nozzle and the mold are integral with the tundish or a molten steel reservoir. In addition, the seal device is of such a construction as to seal the jointed portions fixed together. Therefore, if it is intended to apply such a seal device to the casting apparatus in which one of the tundish and the mold is movable, the seal device must be incorporated into the casting apparatus each time the tundish and the mold are connected together, and this requires much labor and time.
Further, the above conventional seal method or device, using the inert gas, is applied to the type of continuous casting apparatus in which the mold is composed of one block. Therefore, the above prior art does not give any suggestion of the seal between the molds where the mold is composed of the front-stage mold and the rear-stage mold.
Further, in the above prior art, if the rear-stage mold is composed of a tubular extension portion (sleeve), the above prior art requires a metal tube covering the tubular extension portion. As a result, the construction becomes complicated, and besides the cast piece is not water-cooled directly by a cooling pipe, so that the cooling efficiency is low.